Euonymus scale insect problem

I have had a fungus problem on my euonymus, but that has been quite well controlled. The real problem now is the aphids. I am enclosing a leaf with the aphids and their trash. I first noticed them two years ago. I sprayed them with several insecticides in rotation and even put hot soapy suds on them. The insects are thriving, getting worse, and spreading.

Unless you can help me, I fear I might need to dig the hedge out.

The insects on the leaf sample are not aphids - they are Euonymus Scale, an insect which is specific to euonymus. In New Mexico, many of our euonymus hedges are infested with this difficult to control pest. Many people have indeed chosen to remove the hedge rather than continue to fight the scale.

Scale insects are particularly difficult to manage because as the insects mature, they settle down to feed on the plant at a single point. They then build a waxy covering over themselves. This covering protects them from the environment and our insecticides. Before they settle down, the juvenile insects are called "crawlers". In the crawler stage they are much more susceptible to application of insecticides.

The insecticides you have been using are not all effective against euonymus scale. There are several insecticides labeled for euonymus scale control; these are the ones you should use. They are all most effective when used against the crawler stage of the scale insect. In New Mexico there may be several generations of these insects each year, so you may have several opportunities to apply these products. When you do use insecticides, it is important to follow the label directions to maximize the effectiveness of the product and to protect yourself and your environment.

To determine if the crawler stage of the scale is present and treatment appropriate, hold a sheet of dark-colored construction paper or cardboard under a branch of your euonymus and sharply strike the branch. Look for small insects crawling around on the paper. With a magnifier you can confirm that these are scale insects if you are familiar with their appearance. The presence of crawlers indicates that treatment is appropriate.

Sanitation, removing fallen infested leaves and pruning severely infested branches, is another important aspect to treatment. The white material on your euonymus leaves are the adult male scale insects. The adult females are brown and more commonly found on the twigs. Removing them by pruning and raking reduces the opportunity for reinfestation following spray treatments.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

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